Each set consists of a metal wedge (the plug), and two shims (the feathers). The feathers are wide at the bottom, and tapered and curved at the top. When the two feathers are placed on either side of the plug, the combined width of the set is the same at both ends.
Multiple sets of plug and feathers are typically used to split a single, large piece of stone. The stone is first examined to determine the direction of the grain and to identify any potential defects. After the location of the intended split is chosen, a line is scored on the surface of the stone. A number of holes are then cut or drilled into the stone face along the scored line approximately 10 – 20 cm apart. Plug and feather sets are then inserted in the holes with the “ears” of the feathers facing the direction of the desired split. The plugs are then struck with hammer in sequence. An audible tone from the wedges changes to a ‘ringing sound’ when the wedges are tight. Between each series of strikes, a pause of several minutes allows the stone to react to the pressure. Eventually a crack appears along the line that was scored on the surface and the stone splits apart. Attempting to split the stone too quickly may cause the stone to “blow out” at the site of the plug or split at an undesirable section. While the stone might be recoverable, it requires additional work.